1. Field of the Invention
This invention relates to tools for attaching connectors to coaxial cables by compressing the connector in a direction parallel to the axis of the cable.
2. Description of Related Art
Coaxial cable is widely used to carry radio and television signals, digital data and the like. A major user of coaxial cable is the cable television industry which uses coaxial cable to carry the signal from a central location to each subscriber.
To make the many connections required for the cable television network requires the installation of numerous coaxial cable connectors. To avoid any interruption in service, it is critical that the connectors be applied properly. Many problems with poor signal quality that require expensive service calls are the result of a connector that was initially installed incorrectly.
Coaxial cable connectors come in a variety of designs, but one relatively recent design is a coaxial cable connector which is secured to the prepared end of the coaxial cable by compressing the connector in a direction that is parallel to the longitudinal axis of the coaxial cable.
Various types of connectors which are attached in this way have been designed. One design includes a collapsible compressible ring which collapses inwardly to secure the connector and make the connection when the connector is compressed axially. Another design uses a front and rear half for the connector which slidingly engage when the connector is compressed axially. These types of axial compression connectors can be contrasted with earlier designs wherein the compression was applied radially inward to collapse a portion of the connector and make the connection between the connector and the coaxial cable.
Within the general category of axial compressed connectors, there are a wide variety of different types of connectors. Each connector may have a slightly different compression distance necessary to fully compress the connector. However, in all designs, it is essential that the connector be fully compressed to ensure that the connection is secure.
To achieve a reliable connection, and in order to provide the force required, a hand tool is used to compress the connector. One problem with prior art tools is the failure of the tool to hold the back half of the connector in alignment with, and squarely perpendicular to, the plunger portion of the tool which provides the compression force. When correct alignment is not maintained, the connector will not be compressed properly. At the same time, it is desirable to keep the hand tool light in weight and inexpensive to manufacture.
Heretofore, compression tools have used a C-shaped frame comprising a back and two legs. In a C-frame design the open portion of the frame defines a compression region within which the connector is positioned. A plunger projects into the compression region through one leg of the C-frame, and the connector is supported against a parallel bearing surface on the opposite leg of the C-frame. The back portion of the C-frame is relied upon and must be strong enough to hold the two legs parallel to each other.
In order to keep the front of the connector square relative to the back of the connector, the back and two legs of the C-frame must be relatively large and strong, making them relatively heavy. Otherwise the frame will distort as the compression forces are applied. Such distortion lets the two legs of the C-frame move away from parallel resulting in an improperly compressed connector that may fail. The present invention addresses this problem through the use of an O-frame which permits a reduction in weight and materials cost, while improving tool rigidity.
Another problem with prior art designs relates to coaxial alignment of the back half of the connector relative to the compression plunger. Even if the plane of the bearing surface upon which the back of the connector is supported remains perpendicular to the axis of the plunger, prior art devices have failed to ensure that the axis of the coaxial cable and the back half of the connector remain aligned with the axis of the compression plunger driving the front half of the connector.
Some early designs for axial compression tools, for example, of the type seen in U.S. Pat. No. 5,435,167 provided only partial support via a U-support for the back of the connector. This allowed the back of the connector to rock out of alignment during the compression operation. Performance is significantly improved through the introduction of the applicant's design incorporating a pair of split base supports which completely encircle the cable and provide a full 360.degree. bearing surface for supporting the back of the connector around its entire parameter. This design may be seen in the applicant's co-pending patent application U.S. Ser. No. 08/733,261, now abandoned, which is incorporated herein by reference.
This design for 360.degree. encircling support has been widely adopted in the industry and reduces the problem with ensuring alignment between the front half and the back half of the connector. However, previous implementations of the 360.degree. encircling support design, have allowed the two split base halves to rotate on their pivot relative to the frame of the tool, even after they are closed. This permits the center of the 360.degree. encircling support to wander away from the axis of the compression plunger even though the bearing surface defined by the split base halves remains perpendicular to the axis of the plunger. This misalignment also results in an improperly compressed connector. The present invention addresses this problem through the use of an integral stop on the split base portions which positions them positively in alignment relative to the axis of the compression plunger.
A further problem with prior art split base 360.degree. support members has been the awkwardness of removing the cable from the encircling halves of the bearing support on the split base portions. If the split base portions close tightly and accurately with a relatively high spring pressure (as is desired for maintaining the alignment and retention of the cable during the compression operation), it is difficult to open the two split base portions to extract the cable from between them.
This problem has been addressed in the present invention through the use of a pair of push surfaces which are located on a side opposite the pivot point of the two split base portions to provide a simple rocker action opening as used in a clothes pin or alligator clip.
Yet another problem with prior art devices relates to the interconnection between the handle providing the compression force and the plunger performing the compression. Typically, as the handles are opened, the plunger is pulled towards the retracted position by a link. Some prior art designs have locked into the open position when the handles open too far and the link passes over center. The present invention addresses this difficulty with an enlarged plunger head which limits rearward motion of the plunger.
A further problem with prior art tools has been the need to use two hands to operate the tool. In such tools, the handle must be manually pulled outward to the open position before it can be squeezed to the compression position. The present invention addresses this difficulty through the use of a spring which automatically opens the handle and a bail which latches the handle in the closed position for storage.
Another difficulty has been the problem with adjusting the compression distance between the compression plunger and the bearing surface on the split base portion. This distance must be maintained and adjusted to compensate for wear and/or to accommodate connectors of different designs. Prior art tools have been awkward to adjust, and misadjusted compression tools result in poor connector attachment. The present invention addresses this difficulty through the use of a simple adjustment and method of locking the adjustment in position, coupled with a gage block which allows the operator to feel the adjustment and turn the adjusting portion of the tool while the gauge block is within the compression region.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a compression assembly tool for axially compressing electrical connectors onto coaxial cables which is light in weight, has low material cost, and is not subject to distortion during the compression operation.
It is another object of the present invention to provide a compression assembly tool which allows the cable and compressed connector to be easily removed from the tool after the connector is compressed.
A further object of the invention is to provide a compression tool which maintains the axis of the co-axial cable in accurate alignment with the axis of the plunger.
It is yet another object of the present invention to provide a tool which is easy to use and which opens automatically, but which can be stored in the closed position.
A further object of the present invention is to provide a design which can be easily adjusted to high accuracy.